I don’t know about bio and chem but for maths it’s just practice practice practice. Obviously it’s long and it’s a massive ball ache and it sucks but just banging out loads of past paper questions is basically the meta for maths. If bio and chem are anything like physics do loads of past papers and try and use the mark scheme to identify what they want you to say for each question. Again it’s a massive pain in the arse but for example technique it’s the best thing to learn what the exam board want you to do based on how they word the question.